Dynamo electric machine



Sept. 1, 1931. H. RIESE DYNAMO ELECTRIC MACHINE F'iled May 27, 1930 Inventor: /e/ r2r/c%1 5/656 Z, W

r i m Patented Sept. 1, 1,931

PATENT OFFICE HEINRICH RIESE, OF ZURICH, SWITZERLAND DYNAMO ELECTRIC MACHINE Application filed. Kay 27, 1930, Serial No. 456,039, and in Germany October 28, 1929.

by the brushes not being replaced in due time so that the brushes are worn out and the spring causing the. brushes to move toward the rotating member, viz. the commutator or slip-rings, makes contact therewith.

The friction and sparking between the 5 ring and the rotating member rapidly estroys it.

Several constructions have been proposed in order to avoid this drawback. But these constructions are either too "complicated especially for small motors, or the opening of the electric current is performed so slowly that sparking of long continuance with all its drawbacks appears.

This invention is adapted to remedy these defects and relates to a device in which when the brushes are worn to a predetermined degree the path of current between the rotatable member and the part electrically connected to the brush and located outward thereof is automatically interrupted by putting an insulating member in this ath of current. With known devices of this kind the interruption of the current is (performed in dependence of, the slow fee of the brush.

In the accompanying drawings are illustrated several examples of construction embod ing the invention.

ig. 1 is an elevation partly in section showing parts of a dynamo electric machine for instance an electromotor provided with a first construction of the device.

Fig. 2 is a vertical cross section, showing parts of Fig. 1,

Fig. 3 is a similar view as in Fig. 2, showlng another construction similar to that of Figs; 1 and 2.

ferring to Figs. 1 and 2, the brush holder is provided with an inner bush 1 of metal or any other conducting material and with an outer bush 2 of insulating material. The bush 2 is arranged in the usual manner in a corresponding hole of the stator shell 7. The brush 3, 3' for instance of rectangular cross section is guided within the correspondingly shaped opening of the bush 1, the portion 3 of the brush made of carbon or any other suitable conducting material making contact with the commutator 4. The portion 3 of the brush being made of an insulating material and secured in any suitable manner to the portion 3 covers the upper portions of the side Walls and the upper front wall of the portion 3. A helical spring 5 engaging a projection 3" of the portion 3' and a projection 8 of a plug 8 of insulating material screwed into an 1nternal thread of the bush 2 acts to carry the brush 3 into contact with the commutator 4. A strip 6 of conducting fusible material for instance of a fuse-alloy, is secured in any suitable manner to one of the lateral walls of the portion 3 of insulating material which at this place is provided with a cor.- respondingly shaped recess to receive the strip 6. The strip 6 makes contact with the portion 3 on the boundary-line 9 between conducting portion 3 and insulating portion 3' and extends upward from this boundaryline for instance 1 to 3 mm. As shown in Fig. 2 the strip 6 is triangular so that its cross section decreases upward with the distance of line 9-.

In operation, as soon as the portion 3 of the brush wears down and the boundaryline 9 leaves the lower edge In of the bush 1, the current flows from the bush 1 through the strip 6 to the portion 3 and the commutator 4. The strip 6 of fusible material is so dimensioned, that it does not melt until only its upper portion makes contact with the bush 1 and theline g is at some distance of the bush 1. By this means the interruption of the current is performed withno sparking or with a sparking of ver short duration. The motor will be broug t to a full stop before the brush has been wholly worn down and the spring 5 is prevented from making contact with the commutator 4. The motor cannot be re-started before the brush is replaced by a new one.

In the form of construction of Fig. 3 the strip 6a of fusible material may be made with equal cross sections at all distances ber, a conductin from the line g. In this'case the strip is so dimensioned that it does not melt as long as it makes contact with the bush 1. In Operation, as soon as the upper edge of the strip 6a leaves the lower edge is of the bush 1 a sparking of short duration will take place between the edge is and the upper edge of the strip 6a,. This sparking rapidly causes the strip 6a to melt whereby the current is interrupted. In the moment of interruption the line 9 is at some distance of the bush 1 so that the interruption of the current will be securedly performed by melting of the strip 6a.

It is obvious that the device of the invention can also be used with machines having slip-rings instead of commutators.

claim 1. In a dynamo electric machine, the combination of a rotatable contact member, a brush member bearing on said contact memher, a conducting member located outward of the brush and normally electrically connected therewith, an insulating portion secured to one of said electrically connected members, a boundary-line being formed thereon between conducting portion and insulating portion, and a fusible member be- .ing secured to the insulating portion of said member comprisinga conducting and an insulating portion, the fusible member making contact on said boundary-line with the conducting portion of this member and being arranged to conduct the current to the rotatable member when the brush has been worn to a certain point.

2. In a dynamo electric machine, the combination of a rotatable contact member, a brush member bearing on said contact member, a conducting member located outward of thebrush and normall electrically connected therewith, an insu ating portion secured to one of said electrically connected members, a boundary-line being formed thereon between conducting portion and insulating portion, and a fusible member being secured to the surface of the insulating portion of said member comprising a conducting and an insulating portion, the fusible member making'contact on said boundaryline with the conducting ortion of this member and being arrange to conduct the current to the rotatable member when the brush has been worn to a certain point, at

'least a portion of the fusible member near said boundary-line being adapted to conduct the motor current without melting.

3. In a dynamo electric machine, the combination of a rotatable contact member, a brush member bearing on said contact memmember located outward of the brush an normally electrically connected therewith, an insulatin cured to one of said electrical y connected members, a boundary-line bemg formed thereon between conducting portion and insulating portion, a spring acting to move the brush toward the contact members, and a fusible member being secured to the surface of the insulating portion of said member comprising a conducting and an insulating portion, the fusible member making contact on said boundary-line with the conducting portion of this member and being arrange to conduct the current to the rotatable member when the brush has been worn to a certain point, the fusible member being constructed to melt by sparking not before it ceases by the feed of the brush to conduct the current to the rotatable member.

4. In a dynamo electric machine, the combination of a rotatable contact member, a brush holder comprising a bush of conducting material, a brush guided in said bush, the brush comprising a conducting portion bearing on said contact member and an insulating portion secured to the conducting portion, a boundary-line being formed on the surface of the brush between conducting and insulating portion, a spring acting to move the brush toward the contact member .and to disconnect said conducting portion of the brush from said bush when the brush has been worn to a certain point, and means for accelerating the putting of the insulating portion of the brush in circuit as compared with the velocity of the automatic feed of the brush by said spring when said boundary-line has left the bush.

5. A brush for dynamo electric machines comprising a conducting portion adapted to bear on a rotatable member of an electromotor, an insulating portion secured to the conducting portion, a boundary-line being formed on the surface of the brush between conducting and insulating portion, and a fusible portion being secured to the insulating portion, making contact on said boundary-line with the conducting portion and extending from the boundary-line some distance on the surface of the'insulating portion.

In testimony whereof I have afiixed my signature.

HEINRICH RIESE.

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